1. Field of the Invention
The invention relates to an improved electrohydraulic valve controller, in particular for controlling a gas exchange valve in internal combustion engines.
2. Prior Art
In internal combustion engines used for driving motor vehicles a fuel-air mixture is compressed and ignited in a work chamber where the energy produced is converted into mechanical work. In such engines, the air, or the fuel-air mixture, is delivered to the work chamber via valves (inlet or intake valves) and to remove the products of combustion from the work chamber via valves (outlet or exhaust valves). Controlling these valves is very significant for determining the efficiency of the engine. In particular, the gas exchange in the work chamber is controlled via the control of the valves.
Besides camshaft control, it is also known to use an electrohydraulic valve controller. The electrohydraulic valve controller offers the capability of variable or fully variable valve control, making it possible to optimize the gas exchange and thus to enhance the motor efficiency [redundant, or “engine efficiency”] of the engine.
The electrohydraulic valve controller includes a hydraulically actuatable control valve, whose control valve piston actuates a valve body of the inlet and outlet valves and leads toward a valve seat (valve seat ring) (closure of the valve) or moves away from it (opening of the valve). The control valve can be actuated by way of controlling the pressure of a hydraulic medium. The pressure control is effected here via magnet valves incorporated into the hydraulic circuit. To achieve gas exchanges that are as optimal as possible, the highest possible switching speeds of the control valve are needed. As a result of these high switching speeds, the valve body of the inlet and outlet valves strikes the valve seat ring at high speed. The result is on the one hand noise, and on the other the valve components are subject to relatively high wear.
In order to reduce the switching speed of the control valve shortly before the valve body strikes the valve seat ring, it is known to assign a hydraulically acting valve brake to the control valve piston. This valve brake is based on reducing a flow cross section for the hydraulic medium, so that a damping action ensues. A disadvantage, however, is that the braking action of the valve brake is very highly dependent on the viscosity of the hydraulic medium, which as a rule is hydraulic oil. The viscosity of the hydraulic medium is in turn highly temperature-dependent. As a result, the valve action of the valve brake and thus the impact speed of the valve body on the valve seat ring is highly temperature-dependent.